SCS is a type of neurostimulation primarily intended to manage chronic pain, particularly within the back, neck, arms or legs. Benefits of SCS or other forms of neurostimulation may include: a reduction in pain; a reduction or elimination of the use of pain medications; and increased activity levels and an improved overall quality of life. Neurostimulation has been used to manage pain that comes from failed back surgery syndrome or post-laminectomy syndrome and other neuropathies. To this end, an SCS system may be implanted within the body to deliver electrical pulses to nerves along the spinal cord. Some patients describe the resulting sensation as a gentle massaging sensation or, in some cases, simply the absence of pain. The SCS system typically includes a small generator device similar to a pacemaker but equipped to send electrical pulses to leads mounted along the nerves near the spinal cord. The generator is usually implanted in the abdomen or buttock area. The stimulation leads may include either thin wires or paddles for delivering electrical pulses to the nerves along the spinal cord. Thin wire leads, also referred to as percutaneous leads, may be implanted within the epidural space. Paddle leads are instead typically implanted during a surgical procedure where a small amount of bone is removed from one of the vertebra. An external controller, similar to a remote control, is provided to allow the patient to control or adjust the neurostimulation.
As such, SCS for chronic pain treatment is essentially a “one way” stimulation system that delivers stimulation with a certain amplitude, pulse width, frequency and duration. The clinician and patient can typically adjust only a few parameters to improve efficacy. There are usually no clear guidelines on what parameters should be adjusted, and by what amount, to improve the SCS. In addition, pain perception can be very subjective. Overtreatment and under-treatment of patients using SCS is also a risk. Perhaps most importantly, conventional SCS systems offer no objective feedback indicative of the efficacy of the stimulation in reducing pain. Still further, the use of SCS for emerging applications, such as an antiarrhythmic therapy or as a sympatholytic agent, may require feedback not based on perceivable pain but rather on objective physiological parameters or measurements. Moreover, issues can arise due to “adaptation,” i.e. the same stimulation effective at implant might not be as effective at a later time.
Accordingly, it would be desirable to provide techniques for more objectively assessing the efficacy of SCS and for controlling further SCS to improve stimulation efficacy and aspects of the invention are directed to these ends. Patients with implantable SCS devices may also have implantable cardiac rhythm management (CRM) devices implanted therein such as pacemakers, ICDs or cardiac resynchronization therapy devices (CRTs). Accordingly, it would also be desirable to provide techniques for allowing pacemakers or other devices to measure quantitative parameters within the patient representative of the efficacy of SCS for use in controlling or guiding further SCS therapy. It is to these ends that other aspects of the invention are directed.